1. Field of the Invention
This invention relates to an apparatus for the selective routing of information signals, and more particularly, to an apparatus including one or more receiving apparatuses for selectively receiving information from a plurality of transmitting apparatuses.
2. Description of the Prior Art
An information transmission system such as monitoring television system uses an electronic switch or an electronic matrix switch as an information signal selecting apparatus for selectively connecting one or more television cameras to one or more television monitors.
An electronic switch or electronic matrix switch are also used for connecting sequentially a plurality of television cameras to a television monitor or a video recorder through a sequential switch-over operation in order to display sequencing images from the plurality of the television cameras on the television monitor or to successively record the images on the video recorder.
However, in a well known electronic switch or matrix switching used for a system of this kind, as the number of television cameras and monitors or video recorders increase, it increases the cross talk between the different information signals as well as increasing the centralized switching and coordination complexity, requiring larger software and hardware capacity to control the multiple individual independent outputs. Thereby, as the system grows, the information signals become corrupted with cross talk and the matrix switching control becomes costly and inefficient.
Further, well known electronic switches or an electronic matrix switches do not employ synchronized switching and the selected images displayed on a monitor are often disturbed during and immediately after the switching-over from one television camera to another.
In such an information switching system it is preferable to mutually lock the internal synchronizing signals of a plurality of television cameras and the electronic switching time to an external synchronizing signal, in order to prevent the picture image on the monitor from being disturbed during and immediately after the switching operation from one television camera to another.
As the one of the devices for synchronizing a plurality of television cameras, there are known apparatus for transmitting vertical synchronizing signal and a horizontal synchronizing signal or composite synchronizing signal used in a television system. Another known apparatus for transmitting a vertical drive signal and a horizontal drive signal, and driving the television camera and its deflection circuits by the transmitted vertical drive signal, and the horizontal drive signal.
In any of the above known methods and devices of the type under discussion, as the transmitted synchronizing signal itself is a train of pulses, which can be easily influenced by noise, the transmission of a synchronizing signal requires the use of a coaxial cable with its high shielding effect, which makes it costly for systems with plurality of television cameras.
Another known apparatus for synchronizing a plurality of television cameras, is an apparatus for transmitting an external synchronizing signal from an external synchronizing generator to the television cameras by injecting the external synchronizing signal into the video signal transmission line and locking an internal synchronizing signal generator of the television camera by means of the transmitted external synchronizing signal. Such an apparatus is disclosed in U.S. Pat. No. 4,603,352 the contents of which are incorporated herein by reference.